1. Why Steamed Pudding Gets Holes When the Heat Is Too Strong
If you stick a spoon into a pudding and find it full of holes, you have encountered "su." Pudding is a dessert made by steaming or baking a mixture of eggs, milk, and sugar until it sets. Originally known as pudding in Britain, it is widely loved in Japan under the name "purin." [6] However, if you apply too much heat, small holes line up in the cut section. These are the "su" holes. Culinary research explains that when egg liquid is heated, proteins shrink and harden at 90°C or higher, pushing the water inside out. That water then evaporates, creating the holes. [1]
When "su" appears, the texture changes too. The sponge-like structure inside becomes tightly packed, and moisture is pushed out. This process is called syneresis. As a result, the pudding becomes hard, and the mouthfeel worsens. [1] So, what temperature should you aim for to stop before the holes form?
2. How Close the Setting Temperature and the Hole-Forming Temperature Are (Only 7°C Apart)
In a culinary research experiment, a mixture of eggs and water (ratio 1:2) was heated from 40°C, and temperature changes were measured. [1] Note that this mixture contained no milk or sugar, so it does not represent the exact values for real pudding liquid. With low heat (rising 2.8°C per minute), setting began at 68°C, completed at 80°C, and holes began to form at 87°C. With medium heat (rising 7.5°C per minute), these temperatures were 71°C, 84°C, and 91°C. [1]
Let’s convert that 7°C gap into time. The difference between fully setting and holes starting to appear is 7°C for both low and medium heat. Assuming the temperature continues to rise at the same rate, that 7°C takes about 2.5 minutes on low heat, but less than 1 minute on medium heat. The same paper notes that while medium heat sets the pudding quickly, the temperature rises too fast, making holes likely. Low heat takes longer but is less likely to cause holes. [1] It is suggested to warm the egg liquid to about 60°C before steaming and then steam at 85–90°C, noting that this is a cooking technique requiring careful temperature control. [1] Real pudding liquid contains milk and sugar. How do these two ingredients move the temperature?
3. How Milk Helps Pudding Set and Sugar Raises the Setting Temperature
A high school lab report from Aichi Prefecture compared puddings made with water and milk using the same method. The milk pudding set, and tasted good, while the water pudding was runny and did not set well. [3] Since this is a student record, we read it as one example.
Looking at the numbers, university research compared setting temperatures by adding 0.5 to 4 times the amount of liquid to 100g of eggs. In all cases, the more the liquid was diluted, the higher the setting temperature became. Milk at 0.5 times set at 69°C, and at 4 times at 72°C, not rising as much as when diluted with water. [2] Prior research suggests that calcium in milk weakens the repulsion between egg proteins. [2] Conversely, adding sugar raises the setting temperature. In this study, with any dilution method, the sugar-added mixture had a higher setting temperature than the mixture without sugar. [2] Under these conditions, egg liquid with milk sets more easily than liquid diluted with water, and sugar raises the setting temperature. But there is another main character under the pudding.
4. How Heating Sugar Until Just Before It Burns Makes Bitter, Fragrant Caramel
When sugar is heated, it first melts into syrup. As heat continues, the color progresses from light brown to dark brown. Science writers explain that around 160°C, sugar decomposes and forms brown substances called "caramel." However, the exact mechanism of this reaction is not fully understood. [4] It is safe to read 160°C as one example of a guideline.
The taste changes too. As heating progresses, what was odorless and sweet gains sourness, bitterness, and a strong aroma. Further heating leads to burning. [4] Caramel is used to flavor pudding. Ezaki Glico explains that for their Pucchin Pudding, they use roasted sugar (heated sugar) for the caramel, providing a subtle bitterness, pleasant acidity, and fragrant aroma in addition to sweetness. [5] We want to eat smooth pudding and bitter caramel together. That is why containers were designed to let the pudding pop out of the dish with the caramel.
SAFETY NOTE: Hot caramel can cause serious burns, so an adult should handle it.
5. How Pudding Changed from Its Meiji Era Beginnings to Containers That Pop Out Smoothly
According to a Gendai Business article, the earliest example of the dessert pudding in Japanese literature is found in Kanagaki Robun’s "Seiyo Ryori Tsu" from Meiji 5 (1872). However, the ingredients listed there include dried persimmons, ginger, mikan, carrots, and rice, which differ from the modern custard type. By Meiji 22 (1889), books like "Wayo Kashi Seihou Dokunai" listed items like bread butter pudding, suggesting people were hearing the word "purin" by then. [7]
Around 1970, there were few desserts in supermarkets, and puddings were popular in local cake shops. Glico developed a pudding where you could eat the caramel and pudding together from the first bite. They created a container where you break a tab to let air in, allowing the pudding to pop out onto a plate. It was launched as "Glico Pudding" in 1972 and renamed "Pucchin Pudding" in 1974. [5]
During development, the company president reportedly said it was okay if sales dropped by half, as long as they made a pudding tastier than competitors. Staff were encouraged by this and modeled the texture on cream puffs. [5] In 2013, the company stated that cumulative sales since launch exceeded 5.1 billion units, earning a Guinness World Record as the best-selling pudding in the world. [5]
6. How to Check the Cross-Section and Tab of a Store-Bought Pudding
Pick one store-bought pudding and break it in half with a spoon. Look at the cut surface to see if there are small holes. If there are, those are "su." If you see no holes, that is the observation. [1]
Before breaking the tab, if the container has one, look for where the air hole is. Breaking the tab lets air in, and the pudding pops out onto the plate. You can also see how the caramel comes out on top. Since this is food, Then enjoy eating it.. [5]
If you want to research more, experiments on setting temperature and holes are published in the research bulletins of Tokyo Kasei University and Otsuma Women’s University. You can read the text from sources [1] and [2] in the reference list. [1] [2]